The present invention relates to a fault detection system that detects a fault or deterioration in a semiconductor module, particularly in an inverter, and to the operation method of an inverter system with a plurality of inverters.
An inverter has been used widely, for example, to save energy in, and increase the functionality of, the power system of a train. One of the important problems of an inverter is to increase the reliability of a semiconductor module in the main circuit. A conventional way to ensure reliability is to make a fatigue test to evaluate performance in order to prevent the semiconductor module from being destroyed during system operation. However, the life of a semiconductor module depends largely on the usage condition and varies widely according to the semiconductor modules. Those problems sometimes result in the sudden destruction of a semiconductor module during system operation and stop the system.
One of main fault modes of a semiconductor module is a semiconductor chip destruction caused by an insufficient radiation. This is caused by a long-time thermal fatigue that generates cracks in the soldering layer attaching the semiconductor chip onto the radiation fin, and those cracks sometimes result in the semiconductor chip being improperly attached. Similar problems have arisen in the semiconductor module of an integrated circuit, such as a CPU, where processing power is significantly increased and the heat generation is a problem.
To solve those problems, JP-A-7-14948 proposes deterioration detection means for detecting a temperature rise in the members of a semiconductor module and, from the change with time, detects deteriorations. JP-A-8-126337 proposes a life estimation method that, with a temperature sensor on a semiconductor module, adds up the thermal stresses actually added to a semiconductor module and, from the resulting value, estimates the life.
The method described in JP-A-7-14948 requires a plurality of temperature sensors, making the detection means in an inverter, composed of a plurality of semiconductor modules, more costly and complicated.
Although the method described in JP-A-8-126337 shows the history of temperatures that caused cracks in the soldering layer, it does not show the degree of deterioration. Another problem is that, because the deterioration of semiconductor modules varies widely, a semiconductor module is sometimes destroyed before the thermal stress reaches the upper limit value. Conversely, a semiconductor module sometimes does not deteriorate at all even when the thermal stress reaches the upper limit. In the latter case, replacing the semiconductor module when the estimated life terminates does not exploit the full capabilities of the semiconductor module.